Field of the Invention
This disclosure relates to an image forming apparatus such as a copier, a printer, a facsimile, or multi-function printer having the plurality of functions, in which an electro-photographic system or an electrostatic recording system is used.
Description of the Related Art
Hitherto, in an image forming apparatus which forms a toner image by using an electro-photographic system, a two-component developing system which uses a two-component developer that is made by mainly mixing a toner and a carrier is widely used. In the image forming apparatus, the two-component developer is borne onto a developing sleeve which is a developer bearing member, and the toner in the two-component developer is supplied to a photoconductive drum which is an image bearing member. A surface of the photoconductive drum is charged to a predetermined charge potential, and an electrostatic latent image is formed by exposing the surface. In addition, by applying a predetermined development voltage to the developing sleeve, the toner which is charged to the same polarity as charge polarity of the photoconductive drum is adhered to the electrostatic latent image, and the toner image is formed.
Here, it is desirable that a difference (Vback) between a potential (Vd) on the photoconductive drum of a non-image portion in which the electrostatic latent image is not formed, and a value (Vdc) of a DC component of the development voltage applied to the developing sleeve, is controlled to be within a predetermined range. In other words, “carrier adhesion” in which the carrier in the two-component developer, which is borne on the developing sleeve, is adhered to the photoconductive drum when Vback is large occurs, and on the contrary, a so-called “fogging” in which the toner is adhered to the non-image portion of the photoconductive drum when Vback is small occurs. In particular, since there is a possibility that the surface of the photoconductive drum is damaged when the carrier adhesion occurs, hitherto, Vback is controlled to prevent the occurrence of the carrier adhesion.
It is desirable that the relationship of Vback is maintained when application of each voltage is stopped in response to image formation completion, i.e., in a case of executing a voltage falling control, and when application of each voltage is started in response to an image formation start, i.e., in a case of executing a voltage rising control. In particular, in the case where the voltage falls, in order to reduce the carrier adhesion to the photoconductive drum, a development voltage and a charge voltage are lowered after rotation drive of the developing sleeve is stopped. Here, after the developing sleeve is stopped, when Vback is applied between the developing sleeve and the photoconductive drum, there is a case where a phenomenon occurs in which the toner in the developer on the developing sleeve is adhered to the developing sleeve due to the influence of an electric field. When the toner adhesion to the developing sleeve occurs, a belt-like image is generated at a sleeve pitch in the next output image. Therefore, JP-A-2010-134205 suggests controlling Vback in order to reduce the toner adhesion to the developing sleeve.